Rectifier and control means therefor



y 1941- M. L. HASELTON ETAL 2,248,321

RECTIFIER AND CONTROL MEANS THEREFOR Filed DeG. 31. 1958 FIG. I

FIG .2

PLATE SUPPLY VOLTAGE RECTIFIED PORTION OF A.C.

CATHODE POTENTIAL AXIS OF A.C. GRID voLTA E (LIGHT LOAD) K NEGATIVE(GROUND) POTENTIAL AUXILIARY GRID POTENTIAL PLATE suPPLY VOLTAGERECTIFIED PORTION CF AC.

ac. OUT PUT" PoTENTIAI f GRID VOLTAGE xIs 0F AG. GRID voLTAGE (Ham Low)-cATHoDE POTENTIAL DC. OUTPUT L POTENTIALA UXILIARY GRID POTEN I LNEGATIVE (GROUND) M. 'F MEEEE- FS POTENTIAL H. F. MAY

ATTORNEY under conditions of wide Patented July 8, 1941 RECTIFIER ANDCONTROL MEANS I THEREFOR Merton L. Haselton, Rye, and Harold F. l\ /Iay,Valley Stream, N. Y.,.assignors to Telereglster Corporation, New York,N. Y., a. corporation of Delaware Application December 31, 1938, SerialNo. 248,788 I Claims. (o1. 175-363) This invention relates toimprovements in rectifiersof the gaseous discharge type and means forcontrolling the ignition or starting time of such rectifiers.

Rectifier tubes of the gas-filled grid controlled type, such, forexample, as those containing an inert gas or mercury vapor or the like,require means for controlling the ignition or starting time of thetubes. Various methods of control for such rectifiers have heretoforebeen employed, one of which methods is to impress on the grid or controlelement of the main rectifier tube an alternating potential of suitablemagnitude and in fixed phase relation to the alternating potentialapplied to-the rectifier anode circuit, and superimposing on saidalternating potential impressed on the control element, a variabledirect current controlling potential, wherebythe ignition time of thetube may be adjustedor varied. The control systems heretofore employed,however, including those of the character described, have not been foundsuitable for automatically maintaining the direct current output voltageof a rectifier at a predetermined constant. value under conditions ofWide and rapid fluctuations of load, such, for example, as a pulsatingload varying from minimum to maximum many times persecond.

When gas-filled grid controlled rectifiers are started from a coldcondition, the arc concentrates at some spot on the cathode instead ofimpinging on the entire cathode surface, and this bombards theactivematerial off the cathode, thus damaging the cathode and shorteningthe life thereof. Heretofore it has been proposed to prevent starting ofthe rectifier until the cathode was properly heated,by opening the pathof the input power supply or the rectified output, but such arrangementshave involved various disadvantages, such as the use of switchingcontacts of large potential or current carrying capacity with resultantarcing of thecontacts and difiiculty of maintenance of suchcirouits.

An object of the invention is a gas-filled grid controlled rectifier inwhich the direct current output voltage is automatically maintained at apredetermined and substantially constant value and rapid fluctuations ofload.

Another objector theinvention is an improved automatic output voltageregulating means for rectifiers of the gaseous discharge type.

A further object is, the provision of more suitable means for balancingthe load between two or more rectifier tubes as, for example, the twotubes in a single phase full wave rectifier.

An additional object is to provide an improved starting means forautomatically preventing the rectifier from conducting current untilafter the cathode has become completely heated.

Various other features and advantages of the invention will be apparentfrom the following detailed description, taken in connection with theaccompanying drawing, in which:

Fig. v1 shows a single phase full wave rectifier and control meanstherefor, embodying the principles of the invention; and

Figs. 2 and 3 illustrate graphically the characteristics of variouscontrol voltages employed in the arrangement of Fig. 1.

Referring to Fig. 1, there is shown a single phase full wave gridcontrolled rectifier circuit having two half-wave rectifier tubes II andI2 with electron emitting cathodes I3 and I4, grids I5 and I6, andanodes or plates I! and I8. The plate supply current for the rectifieris obtained from a source of alternating current connected to theprimary winding I9 of the supply transformer, the secondary 20 of whichis connected across the plates of the rectifier tubes. The secondaryplate supply winding of the transformer is tapped at the center ofwinding 20 and this center tap is connected to a filter choke 2|; theother end of the filter choke 2| is connected to one side of the filtercondenser 22, and one side of a load 23. The load circuit is completedthrough the filament or cathode circuit of tubes II and I2, includingthe hot cathodes I3 and I4 connected across the secondary filamentsupply winding 12 of the main transformer. The winding I2 is preferablymiddle tapped for connection to the external load circuit, as shown, theconductors I3 and I4 from the winding '12 being connected at 13' and I Ito the two filaments or cathodes I3 and M.

The above circuits comprise a single phase full wave rectifier of theconventional type, withthe exception that the filter choke 2|,ordinarily placed in the cathode circuit, has been placed in the anodeplate circuit in. order to avoid having the voltage drop across thechoke appear in the grid control circuits of the tubes, as will beexplained later. It is desirable, in order to secure relatively stablevoltages under conditions of rapidly fluctuating loads to make thefilter choke 2| of relatively low impedance and filter condenser 22 ofrelatively large capacity.

The tubes II and I2 are filled with xenon, argon or other inert gas,although mercury or at any point in the firing range of the tubes, whichapproaches the limitsof zero and 180 degrees on the positive half cycleof the supply current, without shifting the phase of the out-ofphasepotential. Furthermore, as is desirable in starting, the tube grids maybe blocked by making the auxiliary control potentialsufificientlynegative so that the tubes will not be permitted the cathode, no platecurrent will flow and, therefore,a uni-directional current only will beim-,

pressed upon the output terminals of the rectifier as load.

Grids l5 and 16 are used tocontrol the starting points of the tubesduring their active periods by'impressing a proper potential upon thegrid, thereby controlling the electron flow from the cathode and thuscontrolling the ionization of the gas necessary to induce the maindischarge between plate and cathode. The means for Him.- pressing theproper potential upon the grid at the desired time are as follows. .Asinusoidal or AC control voltage is generated by transformersecondarywinding 24 which may be on-the main supply transformer. Acrossthe terminals of this secondary winding is connected aphase shiftcircuit consisting of resistance and capacity 21.

The value of the resistanceand capacity is so chosen as to provide acontrol voltage across the terminals 28 and 29 of the phase shiftcircuit which will lag the main supply voltage by approximately 90degrees."- In the illustrative embodiment shown, with a 1-10 volt powersupply, the capacity 21 is of the order of y microfarad, and. theresistanceis of'the order of. 7500 ohms. The particular values will, ofcourse, de-

' pend'upon the various constants of, and potentials employed in, thecircuit, and also upon the desired manner of operation of the rectifier.It will be understood that an inductance might be used instead of thecapacity to provide the necessary degree of phase shift; -Apotentiometer 30, with slide 2|, is connected across the output of thephase shift circuit 28 and 29. -The' output terminals of the phase shiftcircuit are also connected through grid resistors 32 and 33-to the gridsl5 and I6 of the rectifier tubes;

By these means a fixed AC potential is imposed on the grids of the twotubes H and. I2, the potential of each grid lagging the plate potentialby a fixed amount and approximately 90 degrees. As the grid potential ineach cycle becomes relatively more positive, the electrons emitted inthe tubes increase until they cause ionization of a sufficient number ofgas molecules to render the tube conducting, at which'time the maindischarge will start; i This discharge will continue during theremainder of the positive half cycle or until the plate supply currentagain passes through zero, when the discharge will cease and the tubewill remain inactive during the negative half cycle. Once the dischargeoccurs,.the,grid is no longer effective to control M the remainder ofthat period, but on the next positive half cycle the grid will againfunction in the same manner to determinethe time of starting.

The slide on the potentiometer 30 provides a point in the gridcontrolcircuit at which an auxiliary control potential may be connected.so that such auxiliary potential is impressed upon the grids, inaddition. to the AC out-of-plrase potentials; By variations ofthisauxiliary control potential, the tubes {maybe adjusted to fire Bymeans of the center tap 3! on potentiometer 3|), the phase lag ACvoltage is divided into two parts, degrees out-of-phase with each other,.and lagging theircorresponding voltages of the .two halves ofthe platesupply transformer winding. It is desirable to make center tap 3|adjustable for the'purpose of exactly balancing the firing points of thetwo rectifier tubes to offset any variation in manufacture or assembly,for if the firing characteristics or grid potentials are notapproximately the same then one or the otheriof the two tubes willconduct more current, and limit the combined capacity of the rectifier;As stated above,the center tap 3| also provides a single point at whichan auxiliary grid potential may be introduced, in a manner hereinafterexplained, for the purpose of advancing or retarding the firing pointsin each cycle. This auxiliary grid potential may be a DC voltagesuperimposed on the AC grid. potential; in effect, toshift theaxis ofthe AC grid voltage or, in other Words, to give the AC grid voltage apositive or negative bias with reference tothe cathode of therectifiers. l

Referring to Fig. 2,.the axis of the AC grid voltage is shown displacedbelow or negative to the cathode potential, the effect being to shiftthe firing point of the rectifiers later in the cycle and causing thereetifiers to conduct current for a shorter time. In Fig. 3 the same ACplate supply and grid voltages are shown with the grid voltage axisshifted above or more positiveflwith respect to the cathode potential.The effe'ctthen is to cause the tubes to fire earlier in the cycle andto. conduct current for a comparatively large portion of the positivehalf cycle. It will'be understood that the construction of the rectifiertubes is such that the tubes break down ant conduct current if the gridis raised to a potential substantially equal to cathode potential duringthe time that the plate anodes are going through the positive halfcycle; that isjin theFigs: 2' and 3, the trigger voltag\is taken to beapproximately cathode potential although tubes with trigger voltagesdiffering from cathode potential would function equally well;

Therefore, by' varying the auxiliary plate potential, ;or superimposedDC grid bias, impressed on point 3| in the grid circuit,the firingpoint. of thetubes may be varied, or ii suflicient negative bias isapplied, the tubes may be blocked-or prevented from firing at all. Theauxiliary circuits'for blocking the grids until the cathodes are hot,and for automatically varying the DC grid bias in order to maintain theDC output voltage constant, will now. be described.

A potentiomleter '34 is connected across .the rectifier outputfthevoltage of which isrequired to be maintained within predeterminedlimits.Slider 35 of the potentiometer 34 is connected to the terminal ofbattery 36, whichprovides a source of reference potential that issubstantially equal and in opposition {to the no-load potential acrossthat portion of the potentiometer 34 between slider 35 and the positiveend of the potentiometer. The negative terminal of the battery isconnected to grid 31 of a vacuum triode tube 36, the function of whichis described later. 'I'he'negative terminal of battery 36 is alsoconnected to the break contact 39 of a relay 40a Relay 40 being normallyin the unoperated position when AC power is first applied to therectifier, break contact 39 is in contact with armature spring 4|, whichis connected to slider 3| of potentiometer 39. V i

A circuit can, therefore, be traced from oathodes l3 and M of rectifiersH and I2, through conductors 13-15, to potentiometer 34, slider 35,battery 36, contacts 39 and 4| of relay 49, slider 3| and potentiometer30, resistances 32 and 33 to grids and I6 of rectifiers H and I2. Itwill be noted thatin this circuit there are two sources ofpo'tential,first the AC potentials across the two halves of potentiometer 39, andsecond the battery 36. In this circuit the voltage of battery 36 is of avalue exceedingthepeak value of the AC voltage wave across one-half ofthe potentiometer 39 and, therefore, the grids I5 and 6 are heldnegative with respect to cathodes I3 and I4, and the grid potentialbelow the trigger voltage, the rectifiers II and I2 are prevented fromfiring during any part of the cycle.

The rectifiers continue to be blocked by negative grid potential untilthe cathodes have become heated sufficiently to prevent damage to theircoatings by cold conduction. Thereafter, the grids are unblocked andtransferred from negative battery potential to automatic controlcircuits by thecombined action of relay 40- and a cam switch 43.

The operation of the relay and cam switch and relay will now bedescribed. The cam switch 43 is operated by a self-starting AC motor 49connected to the main power supply, the circuit including break contacts44 and 45 on relay 40 in parallel with break contacts 46 and 41 operatedby follower 48 on cam switch 43. The motor 49 is geared to cam 43 sothat the cam makes one revolution in approximately twice the normalheating time of the cathodes of main rectifiers H and I 2. The camswitch is provided with two followers48 and 59 displaced around thecircume ferenceof the cam by approximately 180 degrees. The cam surfacehas one depression 43', giving each of the two followers one operationwith a comparatively short dwell during each revolution. The operationof follower 59, and consequent closure of contacts 5| and 52, will,there fore, occur before the operation of follower 48 by approximatelythe heating time of the cathodes 3 and 4, the direction of rotation ofthe cam 43 being indicated by the arrow.

When the primary H! of the power supply transformer 20 is energized, themotor 49 starts, being connected in parallel with the power supply,through contacts 44 and 45 of relay 46. Some time thereafter the camdepression allows follower 59 to operate and close contacts 56 and 52 ofthe cam switch. This causes relay 40 to operate and lock with currentsupplied by an auxiliary vacuum tube rectifier 53. The auxiliaryrectifier 53 preferably is of the full-wave type having. cathodes 54 and55 heated by a separate winding 56 on transformer 29, the conductors 11and 18 of the winding being connected to terminals 11' and 18' of thefilaments or heater elements 19 and 86 of the tube 53. 'I'heplateanodes. 51. and 59 are in parallel with plates I1 and |6..of' the mainrectifier and areconnected to the. maintransformer secondary. A separatefilter condenser 59 connects the auxiliary cathodes 54 and 55 to themaincathode circuit, the purpose of which is to smooth out ripples in theoutput voltage of the auxiliary rectifier. As stated above, upon closureof contacts 5| and 52 of cam switch 53, DC current from the auxiliaryrectifier flows over the circuit, condenser 59, conductor 69, contacts52 and 5| of cam switch 43, winding of relay 40, and conductor 6|, tothe other side of" condenser 59. The condenser 59 being maintainedcharged by the action of auxiliaryrectifier 53, the re'lay40 operates.Upon theoperation-of relay 46, its contacts 44 and in the motor supplycircuit open, the circuit being kept closed bythe parallel contacts 46and 41 ofcam switch 43. Also, armature spring 4| of relay 40 is movedfrom break contact 39 to a make contact 62, thereby transferring thegrid blocking circuit for negative battery through breakcontact 63,spring 88 controlled by the cam follower 48, contact 62 and armaturecontact 4| to slider 3| of potentiometer 36. Furthermore contacts 64 and65of relay 46 close, preparing a locking. path for the relay. Therefore,as the relay operates the grid blocking circuit is maintained and themotor continues. to revolve the cam '43. As follower leaves the camdepression, contacts 5| and 52 reopen and relay 40 remains locked overthe circuit, positive side of condenser 59, conductor 60, contacts 64and 65 of relay, resistance 66, winding of relay 48, to conductor 6| andnegative side of condenser 59.

As the cam 43 continues to revolve, cam follower 48 is engaged by thedepression thereby opening contacts 46' and 4'! and stopping the motor49. At the same time cam follower 48 transfers the grid circuit fromnegative battery on contact 63 to make contact 61, thereby unblockingthe grid and placing the grid circuit under automatic control of theoutput voltage of themain rectifier.

As. described above, the slider 3| on potentiometer 38 provides a pointwhose potential represents the axis of the AC grid control voltage, andatthis point, therefore, the auxiliary control voltage is applied tomove the axis of the AC grid potential up or down; that is, towards the7 positive or negative with reference to the cathode or triggerpotential of the main rectifiers H and II. By this introduction of anauxiliary control voltage and the consequent shifting of the axis of theAC grid potential, the main rectifier tubes are caused to fire earlieror later in the cycle and thereby regulate the current passed by therectifiers to balance the load current.

The variable DC potential for grid control is provided by the dropacross a fixed resistance 68 which is in series with the plate circuitof amplifier triode 38. The heater elements 82 and 83 of the tube areconnected at 13" and 14" to the conductors 73 and 14 of the heatersupply winding 12 of the main transformer. The series regulating circuitis as follows: Positive side of condenser 59, conductor60, contacts 64and 65 of relay, resistance 66, conductor 69, plates 70 and H of vacuumtube amplifier 38, cathode 42, conductor 65, potentiometer 34 or load 23to negative side of condenser 59. The positive end of this seriescircuit being connected to the auxiliaryrectifier53 and condenser 59ismaintained at a-potential higher than that of the main rectifiercathodes I3 and 4, which may be explained by the fact that the auxiliaryrectifier acts asa peak rectifier and the choke coil 2| developsaninductive potential higher than the transformer potential under heavyloads. While the values of the choke 2| and condenser 59 may be variedwithin wide limits, a choke having an inductance of the order of .0125henry and a condenser having acapacity of the order of 4 microfaradshave been found satisfactory. The ,se: ries circuit includes the sourceof outputpoten tialof the main, rectifier developed across 1 thecondenser 22 and load23, which is a constant one,end, th e negative, ofresistance 68.,isgcon-9 nected'through make contact 61, I cam followerspring, contacts 62 and 4| of relay 40 to slider 3| which is theregulating point of the grids l and 16 of the main rectifier. Therefore,ifmthe current passed by tube 38 is increased, the voltage drop throughresistance 68 is increased and the potential of control point 3| is.mademore negative. Aswillbe noted, grid 31. is connected to negative ofthe bucking battery 36, the positive endoi the battery being connectedto slider 35 ofpotentiometer 34. The slider 35 isnormally adjusted sothat grid 31 of tube 38 ,is maintained at a small negative potentialwith reference to cathode 42, this value also being such that .the platecurrent is just sufficient to maintain the. proper potential at controlpoint 3L. v If now the voltage across potentiometer 3.4be momentarilydecreased, grid 31 is immediately carried to, a more negativepotentialwithireference to cathode 42. Practically instantaneous.- lythe current in the plate circuit :is. decreased, the. voltage dropthrough resistance 68 is decreased and control point 3|, the axis oftheAC grid potential, is carried to, a more positive value. Theresult isthat the main rectifier tubes H and I2 on the next and succeeding cyclesfire earlier and pass more current tending to; raise the average voltageof condenser22, and thereby maintain or restore the voltage acrosspotentiometer 34 to nearly its predetermined. constant value. The actionof the control circuit thus automatically advances or retards thegfiringpoint of the main rectifier tubes so that-the current passed by thetubes is increased, or decreased with voltage drops at the DC outputterminals due to fluctuations in load. Because ofthe amplifieraction oftube 38 the voltage shift'ofthe axis of AC grid control voltage, is,manytimes the amount of corresponding variations of output voltage and,therefore, the output, voltage variation between no load and full. loadmay be kept at a minimum; provided the drop in the rectifiers and supplycircuits does not limit the maximum power available, to lessthaniullload value.

' If, the powersupply to the rectifier is interrupted even momentarily,condenser 59 rapidly loses'its charge and relay 4D releases. Thisimrnediately places. negative battery- .on, control point 3| through itsbreak contacts '39 andAlf,

blocking. the main rectifier tubes as, previously described. Relay] 40in releasing also closes its contacts 44 and 45, preparing the supplycircuit of thefsynchronous motor'49 forre storatioi of powersupply. Thestarting circuit is then in a condition to recycle and start therectifier by unblockinglthe grids only after the heatingtime ofthe-tubes has elapsed, as previously described.

,Theystarting circuit is thus made automatically gridsfioating orwithpositivepotential, the DC output volta'geitends; to rise to avaluewhich might; damagecondenser 22 or load, 23. This condition isprevented by relay 40, which may be; adjusted to. drop out ifthepositive (cathode) output potential raises to or above a predeterminedvalue It will be noted that the windingor relay is connected toacircuit, one end or-which is the positive side of condenser 59., the DC"potential'of which is substantially fixed by,theAGvoltageapplied to theplates 51 and58, this AC power supply being substantially constant:.under normal conditions of operation, The other end of the relaycircuit is connected to the positive DC output of the main rectifier.Hence, the current in relay winding viii is the result of the differencebetween the normallyhigher and fixed positive DC potential oithe-auxiliary rectifier and the positive potential oi the DC output. If nowthe, DC output potential of the rectifier increases, the current intherelay winding decreases and depending uponthe adjustable mechanical loadon the relay and the value of locking resistance 66, will release if thedecrease is continued to a predetermined value, In this manner the relayserves as a protectionagainst high :voltage output of the rectifier.

" Any variation in the voltage of the battery will be reflected in analmost proportional variation in the output voltage of the rectifier. Itmay be noted that normally the battery is connecte'd'to negative gridsonly and, therefore, the

current drain on the battery is negligible, tendngtowamga long life withinfrequent renewals required. "Over a period of time the output voltage;if .required, may] be corrected manually within'the regulating limits oftube 38 by slider 35ionrheostat34. S

"Itwill be understood that the single phase, iull wave" rectifier, hasbeen shown by way of example only, and that half wave or three phaserectifierslmay be controlled in a similar manner.

. While there is shown and. described herein acertain'preferredembodiment of the invention, many otheriand variedforms and uses will present themselves to those versed in the artwithout departing from the invention, and the invention, therefore, isnot limited except as indicated by the scope of the appended claims.

re im i l i 1 Analt rnating current rectifier systemcomprisingagasfilled grid controlled rectifier having main discharge anode andcathode electrodes and" a control electrode, 1 a source "of alternatingcurrent supply connected to the rectifier input circuit, and. controlmeans for impressing upon the control electrode an alternating potentialof thel same frequency as, but out of phase with, the potential of saidsupply current, said controlineans also including means. for impressingupon saidcontrol.electrode an auxiliary potential. and means for varyingthe auxiliarypotential to control the firing point of the rectifierduring each active cycle thereof, said last namedmeans comprising animpedance in the output circuit ofthe rectifier for producing apotential that varies with the rectifier output potential, a source offixed reference potential connected in circuit withsaid impedance inopposition to the potential-produced by said impedance and a thermionictube having its grid circuit controlled by the impedance and source offixed reference potential, means comprising a reactance in circuit withthe main rectifier output circuit and an auxiliary rectifier'in circuitwith said reactance for applying to the plate circuit or said thermionictube a potential invariably higher than the potential of the rectifieroutput circuit to increase the range of control and sensitivity of therectifier control circuit, means including said thermionic tube forproducing a potential that varies with the thermionic tube plate'current, and means for impressing the last named potential on saidrectifier control electrode.

2. An alternating current rectifier system comprising a gas filled gridcontrolled rectifier having main discharge anode and cathode electrodesand a-control electrode, a source of alternating current supplyconnected to the rectifier'input circuit, and control means forimpressing upon the control electrode an alternating potential of thesame frequency as, but out;of phase with, the potential of said supplycurrent, said control means also including means for impressing uponsaid control electrode an auxiliary potential, and means for varying theauxiliary potential to control the firing point 'of the rectifier duringeach active cycle thereof, said last named means comprising means in theoutput circuit of the rectifier for producing a potential that varieswith the rectifier output potential, a source of direct current incircuit with said impedance and a 'thermionic tube having its gridcircuit'controlled bythe impedance and source of direct: current, an'auxiliary rectifier having its anodes connected in multiple with themain discharge anode electrodes, a condenser in circuit withtheauxiliary rectifier cathode circuit, and means including saidauxiliary rectifier and condenser for applyingto the plate circuit ofthe first named thermionic tube a potential invariably higher than thepotential of the rectifier output circuit to increase the range ofcontrol and sensitivity of the rectifier control circuit, meansincluding said thermionic tube for producing a' potential that varieswith the thermionic tulo e, plate current, and means for impressingthelast named potential on saidrectifier control electrode. i l 3. Analternating current rectifier system comprising a gas filled gridcontrolled rectifier having main discharge anode and cathode electrodesand a control electrode, a source of alternating current supplyconnected to the rectifier input circult, and control means forimpressing upon the control electrode an alternating potential of thesame frequency as, but out of phase with, the

- potential of said supply current, said control means also includingmeansfor impressing upon said control electrode an auxiliary potential,and means for varying the auxiliary potential to control the firingpoint of the rectifier during each active cycle thereof, said last namedmeans comprising means in the output circuit of the rectifier forproducing a potential that varies with the rectifier output potential, asource of direct current in circuit with said impedance and a thermionictube having its grid circuit controlled by the impedance and 'source ofdirect current, means comprising an inductance in circuit with the mainrectifier output circuit and an auxiliary rectifier and a condenser incircuit with said inductance for applying to the plate circuit of thefirst named thermionic tube a, potential that varies with the rectifieroutput current, means including said thermionic tube for producing apotential that varies with the thermionic tube plate current, andmeansfor impressing the last named potential on said rectifier controlelectrode.

4. An alternating current rectifier system comprising a gas filled gridcontrolled rectifier having main discharge anode and cathode electrodesand a control electrode, a source of alternating current supplyconnected to the rectifier input circuit, and control means forimpressing upon the control electrode an alternating potential of thesame frequency as, but out of phase with, the potential of said supplycurrent, said control means also including means for impressing uponsaid control electrode an auxiliary potential, and

' means for varying the auxiliary potential to control the firing pointof the rectifier during each active cycle thereof, said last named meanscomprising an impedance in the output circuitof the rectifier forproducing a potential that varies with the rectifier output potential, asource of direct current in circuit with said impedance and a thermionictube having its grid circuit controlled by the impedance and source ofdirect current, means comprising an auxiliary rectifier having itsanodes connected in multiple with the main discharge anode electrodesand an inductance in circuit with the main rectifier output circuit anda condenser in circuit with the auxiliary rectifier cathode circuit forapplying to the plate circuit of the first named thermionic tube apotential which varies with the main rectifier outputcurrent butinvariably is higher than the potential of the main rectifier output toincrease the range of control and sensitivity of the rectifier controlcircuit, means including said thermionic tube for producing a potentialthat varies with the thermionic tube plate current, and means forimpressing the last named potential on said rectifier control electrode.i

5. An'alternating current rectifier system comprising a gas filled gridcontrolled rectifier having main discharge anode and cathode electrodesand a control electrode, a sourceof heating current for the cathode, asource of alternating current supply for the rectifier input circuit,and control means for impressingupon the control electrode analternating potential of the same frequency as, but out of phase with,the potential of said supply current, said control means also includingmeans for impressing upon said control electrode an auxiliary potentialand means for varying the auxiliary potential to control the firingpoint of the rectifier during each active cycle thereof, a synchronousmotor device and means for connecting the motor device to said source ofalternating current to energize the device, cam structure controlled bysaid motor device, and means including circuit controlling contactmembers controlled by said cam structure for preventing the passing ofcurrent by the rectifier until its cathode is heated to its normaloperating temperature.

6. An alternating current rectifier system comprising a gas filled gridcontrolled rectifier having main discharge anode and cathode electrodesand a control electrode, a source of heating current for the cathode, asource of alternating ing temperature.

current supply for the rectifier input circuit, and control means forimpressing upon the control electrode an alternating potential of thesame frequency'as, but out of phase with, the potential of said supplycurrent, said control means also includingrmeans for impressing uponsaid control electrode an auxiliary potential and means for varying theauxiliary potential to control the firing point of the rectifier duringeach active cycle thereof, comprising means in the output circuit of therectifier for producing a first potential that varies with the rectifieroutput potential, a source of reference potential in circuit with saidlast named means and having its potential substantially equal and inopposition to the potential produced by said means in the outputcircuit, means controlled by the resultant potential of said firstpotential and said reference potential, means including said last namedmeans for producing a potential that varies with the thermionic tubeplate current, means for impressing the last named potential on saidrectifier control electrode, and means for utilizing said. source ofreference potential for blocking the grid of" said, rectifier until thecathode of the rectifier is heated to its normal operating temperature.l

7. An alternating current rectifier system'comprising a gas filled gridcontrolled rectifier hav ing main discharge anode and cathode electrodesand a grid, a source of heating current for the cathode, a source ofalternating current supply for the rectifier input circuit, and controlmeans for impressing upon the grid an alternating potential of the samefrequency as, but out of phase with, the potential of said supplycurrent,jsaid 7 control means also including means for impresse ing uponsaid grid an auxiliarypotential and means for varying the auxiliarypotential to controlthe firing point of the rectifier during each activecycle thereof, and means for applying to said grid a negative potentialsufficiently high to prevent the passing of current by the rectifieruntil the cathode is heated to its normal operat- 8. An alternatingcurrent rectifier system cornprising a gas filled grid controlledrectifier having main discharge anode and cathode electrodes and acontrol electrode, a source of altere nating current supply for therectifierv input circult, and controlmeans for impressing upon thecontrol electrode a voltage comprising an alter nating potential .of thesame frequency as the potential, means including said thermionic tubefor producing a potential that varies with the thermionic tubeplatecurrent, means for combining said last named potential ,with, andin opposition to, the rectifier output potential to produce .a netpotential which may be either negative or positive with respect to themain rectifier cathode depending upon the magnitude of the voltage dropin the main rectifier output circuit, and means for impressing said netpotential on said rectifier control electrode. 3

9, An alternating current rectifier system comprising a gas filled gridcontrolled rectifier having main discharge anode and cathode electrodesand a control electrode, a source of alternating current supply for therectifier input cir- 'cuit, and control means for impressing upon thecontrol electrode a voltage comprising an alternating potential of thesame frequency as the potential of said supply current and a directpotential variable to control the output voltage, and means for varyingsaid direct potential to control the, firing point of the rectifierduring each active cycle thereof, comprising a source of fixed referencepotential, adjustable voltage divider means in the output circuit of therectifier for producing a first potential substantiallyequal to and inopposition with saidfixed reference potential, said first potentialvarying in accordance with the rectifier output potential, a thermionictube having its grid circuit controlled by the resultant potential ofsaid first potential and said reference potential, means including saidthermionic tube for producing a potential that varies inversely with thethermionic tube plate current, means for combining said last namedpotential with, and in opposition to, the rectifier out-put potential toproduce a net potential-which may be either negative or positive withrespect to themainrectifier cathode depending upon the magnitude of thevoltage drop in the main rectifier output circuit, and means forimpressing said net potential on said rectifier control electrode.

potential of said supply current and a direct potential variable tocontrol the output voltage, and means for varying said direct potentialto control the firing point of the rectifier during each active cyclethereof, comprising a source of fixedreference potential, voltagedivider means in the output'circuit of the rectifier for producing afirst potential substantiallyequal to and in opposition with said fixedreference potential, said first potential varying in accordance with therectifier output potential, a thermionic tube having its grid circuitcontrolled by the resultant potential of said first potential and saidreference 10. In the art of gas filled grid controlledrectifiers ofalternating current, means for regulating the firing point of therectifier during each active cycle by variation of a reversible D. C.component superposed on theA, C. voltage applied to the control gridcomprising adjustable means in the output circuit of the rectifier forproducing potential that varies with the rectifier output potential, asource of fixed reference potential in circuit with said adjustablemeans and having its potential substantially equal and in opposition tothe potential produced by said adjustable means, a thermionic tubehaving its grid circuit controlled by the resultantpotential of, saidfirst potential and said reference potential, and means for "combiningthevoltage drop across said thermionic tube with the output voltage ofthe rectifier for producing the said reversible D. C. componentsuperposed on the A. C. control grid voltage' MERTON Ii. HASELTON.HAROLD F. MAY. 1

